Antarctic Ice Grows as Arctic Ice Declines

With stories of melting glaciers and sea ice dominating the headlines, it may come as a surprise to some to hear that Antarctica - defying the unlucky fate of its northern cousin - has actually gained over the last two decades. Indeed, while scientists noted declines in the amount of sea ice between 2000 and 2002, satellite records have pointed to a steady half a percent yearly gain since 1978.

Climate models have consistently shown that Antarctica has responded much more slowly to global warming than has the Arctic. As Stephen Ackley, a scientist at the University of Texas, San Antonio, put it: "Arctic sea ice is well ahead of the models, and Antarctic sea ice is well behind what the models project." More recent studies have also determined that - outside the tropics - Antarctica displays the strongest climate response to the El Niño-La Niña cycles, suggesting the presence of many important feedbacks between sea levels, ice and air in the Southern Ocean that have yet to be elucidated - and serve to cloud the current climate picture.Despite the gains of Antarctica's sea ice, the larger region - encompassing the Bellingshausen and Amundsen Seas - has suffered as a whole: glaciers in these seas, which flow from the West Antarctic Ice Sheet, are now losing ice to the sea faster than they are being replenished. This "very big threat to glacier ice," as Columbia University's Xiaojun Yuan calls it, could be the result of warm water upwelling near the coast - a consequence of global warming's impact on regional wind patterns.

So what's to account for the differences between Antarctica and the Arctic? Large geographic and oceanographic differences between the poles - an open sea in the south versus an almost landlocked sea in the north - facilitate the buildup of long-lasting, multiyear ice in the Arctic, as opposed to thin, seasonal ice in the Antarctic. As a result, scientists explain that accurately ascribing long-term trends in ice cover to both becomes very difficult. Some recent studies have posited that bacteria and algae living in the ice could trigger the production of large amounts of dimethyl sulfide, thus potentially limiting global warming's effect in the region.

According to the latest models, the Antarctic sea ice will start to gradually decline over the course of the century. Scientists will be keeping a close eye on the mass of Antarctica's sea ice over the coming months; because ice in the Arctic started to melt from underneath before any major changes were noted, scientists want to ensure that they don't miss crucial shifts in the sea ice that a satellite picture might not pick up on.